The Dominican Republic said it would seal its border with Haiti on Friday morning amid a conflict over access to a river shared between the two historically contentious neighbors. The move would further isolate Haiti, a nation that has descended into gang violence and growing hunger.

Tensions have grown in recent days over construction in the Massacre River, which straddles both nations.

President Luis Abinader of the Dominican Republic, who claimed that the excavation of a canal on the river in Haiti would harm Dominican farmers, froze Haitian visas this week and threatened to close the more than 220 miles of border if the two sides did not reach a resolution.

A Haitian delegation met with the Dominicans in Santo Domingo, the capital, on Wednesday for 11th-hour negotiations, but there was no apparent resolution, and on Thursday, Mr. Abinader announced his decision to shut the boundary between the two Caribbean island nations starting at 6 a.m. local time Friday.

“The entire border of the Dominican Republic, both land, sea and air, will be closed,” Mr. Abinader told reporters as he stood in a military base in Santo Domingo among 20 armored vehicles that he said would soon be dispatched to the border. “The Army, the Navy and the Air Force will be prepared to comply with this decision.”

The Haitian government on Thursday evening released a statement saying it “can sovereignly decide on the exploitation of its natural resources.”

The government said it has “the full right” to access the Massacre River, according to the statement, and also called for calm in the wake of the potential border closure.

The decision is likely to deepen the economic turmoil in Haiti, where nearly half of the population is at risk of starvation, according to the United Nations. More than 25 percent of Haiti’s official imports come from the Dominican Republic, though another large share of goods, including food, enters unofficially along the porous border, according to a report from the International Monetary Fund.

Haiti is heavily reliant on trade with the Dominican Republic, as well as the United States, according to the U.S. Department of Commerce. Haiti is the Dominican Republic’s third-largest trading partner.

“Haitians are already in a very difficult position in terms of food security and I’m anticipating this will exacerbate that problem,” said Daniel Foote, the Biden administration’s former special envoy to Haiti. “It’s going to have a particular negative impact on these desperate people who are barely surviving.”

Closing the border between the two countries could also hurt the Dominican Republic since so many of the country’s goods are destined for the Haitian market.

“This border closure generates an evident lose-lose situation,” said Antonio Ciriaco, an economist at the Autonomous University of Santo Domingo. The Dominican Republic also relies on Haitian laborers who cross into the country every day to work in industries like agriculture and construction, he added.

The Dominican Republic last closed its border with Haiti after the assassination of the Haitian president, Jovenel Moïse, in July 2021.

Mr. Abinader has since occasionally closed parts of the border and begun constructing a wall between the two nations after violence escalated in Haiti. Dominican officials said they sought to stop the smuggling of weapons and illegal crossings into the Dominican Republic.

On Thursday morning, Dominican military forces were already gathering on the border.

The use of the Massacre River, named for a bloody battle between Spanish and French colonizers in the 1700s, has long been a source of tension between the two nations. The river was also the site of a massacre of thousands of Haitians by Rafael Trujillo, the Dominican dictator, in 1937.

In 2021, Haiti and the Dominican Republic issued a joint declaration acknowledging a 1929 agreement between the nations establishing that both countries had the right to use water from the river.

The excavation of the river, Mr. Abinader said, was not sanctioned by the Haitian government and was being carried out by former politicians and local businessmen. Dominican officials said the unauthorized construction was another example of the rising disorder in Haiti and the government’s lack of control over the country.

Some water experts said they believed the Dominican government was overreacting given that there are 11 existing canals on the Dominican side of the Massacre River.

“I think it is something that has been completely blown out of proportion, where the political is reigning more than the technical,” said Martín Meléndez, an engineering professor at the Santo Domingo Institute of Technology, adding that Haitians “have the right” to draw water from the river, too.

“This can be resolved taking turns as to who is going to take water, on what day, and how much,” Mr. Meléndez said.

The United States embassy in Santo Domingo issued a warning to American citizens in Haiti that the United States would not be able to help them reach the Dominican Republic in the event of a border closure.

Mr. Abinader said the border would stay shut “for as long as it takes for this provocative action to be eliminated,” and that the closure would be enforced by the military and the national police.

“The Haitian government itself has admitted to having problems controlling its territory,” he said. “And, if there are uncontrollables there, they will be uncontrollable for the Haitian government, but they will not be uncontrollable for the government of the Dominican Republic.”

But Jean Brévil Weston, the leader of a farmers’ group in Haiti that is working on the construction in the canal, said no one in the Haitian government had told any of his members to cease work. And they had no plans to stop doing so.

“We get water or death,” he said in an interview with Magik9, a Haitian radio station. “If we don’t find water for agriculture in the plain, we are already dead.”

Harold Isaac contributed reporting from Port-au-Prince, Haiti, and Emiliano Rodríguez Mega from Mexico City.

By mrtrv